The development of a reliable anticollision system has been retarded principally by inadequate signalling systems to encode the large amount of information which must be transmitted between oncoming aircraft which may be closing as much as 4000 miles per hour (6451 kilometers per hour) and to allow the analysis of the information in sufficient time for the pilot manually or by automatic means to make the corrective maneuver. This limitation in part is due to the necessity of binary coding alpha-numerics and to transmit a long train of bits with the problems of framing, synchronization, parity check, all associated with digital data transmission systems.
It has long been known that a single pulse length can represent a single digit or letter, however the reliable detection of pulse length, particularly after transmission of pulses through a medium in which the leading trailing edges are distorted, can make reliable detection impractical. By reason of this, pulse length modulation has not achieved broad acceptance.
Extensive studies have been made of the effect of transmission medium of single pulses and these have been reported in the literature. Particular reference has been made to helical transmission lines.
Representative of the prior art known to the applicant are
(1) RCA Review, June 1961, pages 219 to 244. "The Helix Parametric Amplifier--A Broad-band, Solid State Amplifier", by C. Cuccia et al.
(2) Proceedings of the IRE, September 1954, "Coupling of Modes in Helixes", by J. R. Pierce et al.
(3) Proceedings of the IRE, December 1959, pages 2099 to 2105, "Coaxial Resonators with Helical Inner Conductor", by W. W. Macalpine, et al.
(4) Proceedings of the IRE, December 1959, pages 2076 to 2084, "Frequency Multiplication with non-linear Capacitors--A Circuit Analysis", by D. B. Leeson et al.
(5) Oscillators by W. A. Edson, 1953
(6) IEEE Transactions On Circuit Theory, Vol. Ct20 5#, September 1973, pages 555-567 @558-9;
Karl Renner et al, on the Design of Wave Digital Filters with Low Sensitivity properties.
(7) "Communication Engineering" by W. L. Everitt, 1932-37, McGraw Hill. Subject: Reflection, pages 128-178; see page 149, FIG. 86.